The present invention relates to an integrated power and attitude control system and, more particularly, to an integrated power and attitude control system that reduces the likelihood of errors in attitude control that can result from power regulation.
Many satellites and other spacecraft, as well as some terrestrial stationary and vehicle applications, such as seagoing vessels, can include one or more energy storage flywheels to provide both a backup power source and to provide attitude control for the vehicle. In such systems, each flywheel is controlled and regulated to balance the electrical demand in the vehicle electrical distribution system, and is also controlled in response to programmed or remote attitude (or torque) commands received by the vehicle main controller. Thus, each flywheel responds to two commands in two distinct parameters, a power command and a torque command. Together, these parameters make up four distinct degrees of freedom. These degrees of freedom are electrical power (e.g., voltage), and momentum about each of three orthogonal axes.
To be controllable, a system needs to have at least as many controllable degrees of freedom as there are uncontrollable degrees of freedom. Flywheels may be implemented in various configurations, which will determine the total number of controllable degrees of freedom for the flywheel. Generally, and as was noted above, the rotational speed of a flywheel provides one degree of freedom, and each flywheel gimbal angle provides another, separate degree of freedom. Thus, for example, a flywheel configured with two gimbals, one gimbal, or no gimbals, will have three, two, or one degree of freedom, respectively.
Some vehicles that have an integrated power and attitude control system include three or more flywheels, each configured with a single gimbal. With this configuration, each flywheel has two controllable degrees of freedom, one degree of freedom for speed and one degree of freedom for gimbal angle. Thus, in a system with three flywheels, six degrees of freedom are available, one gimbal angle and one spin rate for each flywheel. As noted above, for a free-flying spacecraft or some other vehicles, only four controllable degrees of freedom are needed. As a result, the system is overdefined, which means there are multiple solutions for any given command set.
A common control technique for the above-described integrated power and attitude control system configuration is to control all of the flywheels to the same speed, and treat this as a single combined degree of freedom to control the power. The three remaining degrees of freedom are controlled by the gimbal angles of the flywheels. This control technique allows the attitude control loop to operate at a reduced rate, and the power loop to operate at a faster rate, which may be needed to provide voltage stability. However, this control technique does exhibit certain drawbacks, such as introducing xe2x80x9ccrosstalk errorsxe2x80x9d from the power loop to the attitude control loop. For example, a change in the rotational speed of a flywheel affects not only the power supplied to or drawn from the flywheel, but the momentum of the flywheel as well. Thus, when power is supplied to or drawn from a flywheel, it can result in generation of an unwanted torque, and a momentary twisting of the vehicle during combined maneuvers and power surges.
Hence, there is a need for an integrated power and attitude control system and control method that does not result in crosstalk errors between power control and attitude control loops, and thus substantially eliminates unwanted torque generation during combined maneuvers and power surges. The present invention addresses this need.
The present invention provides an integrated power and attitude control system and control method that substantially eliminates unwanted torque generation during combined maneuvers and power surges.
In one embodiment, and by way of example only, an integrated power and attitude control system includes a controller and an energy storage flywheel system. The controller is coupled to receive at least a torque command signal and a power command signal and is operable, in response thereto, to supply (i) a gimbal angular velocity command based at least in part on the torque command signal and (ii) a flywheel acceleration command based at least in part on the torque command signal and the power command signal. The energy storage flywheel system is coupled to receive the gimbal angular velocity command and the flywheel acceleration command from the controller and is operable, in response thereto, to (i) move on a gimbal axis at the commanded gimbal angular velocity and (ii) accelerate on a spin axis at the commanded flywheel acceleration.
In another exemplary embodiment, a method of controlling the relative attitude and rotational speed of a flywheel includes receiving a torque command signal and a power command signal. A gimbal angular velocity command, based at least in part on the torque command, is supplied, and a rotational acceleration command, based at least in part on the torque command signal and the power command signal, is supplied. The flywheel is moved on a gimbal axis at the commanded gimbal angular velocity, and is accelerated on a spin axis at the commanded rotational acceleration.
In yet another exemplary embodiment, a satellite includes a controller and a plurality of flywheel systems. The controller is coupled to receive at least a torque command signal and a power command signal and is operable, in response thereto, to supply (i) one or more independent gimbal angular velocity commands based at least in part on the torque command signal and (ii) one or more independent flywheel acceleration commands based at least in part on the torque command signal and the power command signal. Each of the flywheels is coupled to receive one of the independent gimbal angular velocity commands and one of the independent flywheel acceleration commands from the controller and is operable, in response thereto, to (i) move on a gimbal axis at the commanded gimbal angular velocity it received and (ii) accelerate on a spin axis at the commanded flywheel acceleration it received.
Other independent features and advantages of the preferred integrated power and attitude control system and method will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.